In the manufacture of translucent containers such as clear or colored glass bottles, it is important to maintain dimensional parameters of each container within design specifications for both functional and aesthetic reasons. For example, it is important that the finish of the container, including particularly the container mouth, possess desired geometric characteristics so that the container can be accepted by automatic filling and capping equipment without damage to the equipment, fracture of the container or jamming of the process line.
U.S. Pat. No. 3,313,409, assigned to the assignee hereof, discloses a container inspection system in which containers are routed in sequence through a plurality of inspection stations at which various geometric and other properties are measured. At one such station, an attempt is made to insert a plug of predetermined size into the mouth of the container. The diameter of the plug is coordinated with the minimum container mouth diameter for mating with container filling equipment, for example. If the plug cannot be so inserted into the container mouth, the container is rejected. At other stations of the inspection system, container dimensional parameters are measured by monitoring the positions of rollers in contact with the container as the container is rotated. However, the inspection techniques that require physical contact with the container are slow, and are subject to mechanical wear of the rollers and plugs, for example. The reciprocating motions needed to bring the plugs and rollers into and out of contact with the container draw substantial amounts of electrical power. Furthermore, physical contact of measuring equipment with the container is not desirable at the so-called hot end of the manufacturing process, at which the containers are still soft.
To address some of the deficiencies of the mechanical inspection techniques so described, U.S. Pat. No. 5,461,228, also assigned to the assignee hereof, discloses an apparatus and method for electro-optically measuring dimensional parameters of a container, such as inside diameter of the container mouth. A light source directs light energy into the container, and a light sensor is disposed with respect to the light source and the container to receive light energy transmitted out of the container through the container mouth. A telecentric lens directs onto the light sensor only light energy transmitted through the container mouth substantially axially of the container mouth. The light energy is focused through an iris onto a matrix array sensor, which develops a two-dimensional image of the container mouth. The matrix array sensor is coupled to image processing electronics for determining or calculating a circle of greatest diameter that will fit within the two-dimensional image of the container mouth, and treating such circle as indicative of the effective inside diameter of the container mouth.
In conventional glassware manufacturing processes, glassware is molded in an individual section machine and then placed while still hot on a linear conveyor for transport to an annealing lehr. After stress relief within the lehr, the glassware is transported to various stations for inspection, filling and/or packaging. The lehr divides the hot end of the manufacturing process in which the containers are molded from the cold end of the process in which the containers are inspected and packaged. The techniques for measuring diameter of the container mouth described above are specifically suited for use at the cold end of the manufacturing process. However, it is desirable to implement inspection at the hot end of the manufacturing process so that information on containers having undesirable variations can be obtained quickly and the process corrected. It is therefore a general objective of the present invention to provide a method and apparatus for inspecting containers, particularly for measuring the inside diameter of the container mouth, that can be implemented at the hot end of the manufacturing process. When the containers are directed onto the conveyor following the molding process, the containers are hot, emitting radiation in both the visible and infrared ranges. As the containers travel toward the annealing lehr, they gradually cool, with the rate of cooling depending upon thickness of the individual portions of the container. For example, the container finish and mouth, which are relatively thin, cool more rapidly than the container bottom and heel which are relatively thick. It has heretofore been proposed to measure infrared radiation emitted by a container at the hot end of the manufacturing process to determine or infer wall thickness of different portions of the container. See, for example, U.S. Pat. Nos. 2,915,638 and 3,356,212.